This multidisciplinary program project research effort on Chagas' disease reflects collaborative work between Brazilian scientists and scientists from Harvard. Two core research units, one laboratory-based and one clinical, have been developed at the Federal University of Bahia, Salvador, Brazil, and a third core unit developed with FioCruz encompasses rural populations in Bahia where Chagas' disease is endemic. The Harvard component operates under the sponsorship of the Pan American Health Organization. A major objective is the elucidation of the natural history of Chagas' disease in an area where the disease is hyperendemic. This is being done by combined clinico-parasitologic-immunologic-entomologic longitudinal studies, particularly in Castro Alves and Riacho de Santana. A second project focuses on cardiac arrhythmias in Chagas' disease as detected by ambulatory electrocardiographic monitoring. Two projects focus on cellular and humoral immunoregulatory processes in Chagas' disease, one in man and the other in a murine model. The objective is to elucidate the determinants of progression or of non-progression of infection with Trypanosoma cruzi.